Danish Cohort Study on Mobile Phone Use and Cancer

The increasing use of mobile phones raises questions about possible adverse health effects, especially about cancer in the head (e.g. brain tumours, eye tumours, acoustic neuroma) , as the exposure to electromagnetic fields is highest in this area. Many studies on this topic lack validity due to short observation periods (time between first use of a mobile phone and possible cancer diagnosis) and small sample sizes.

The Danish study is among the largest ones worldwide in the field

In Denmark a cohort study relating to this subject was conducted. All Danish citizens whose first mobile phone subscription was between 1982 and 1995 were selected for the study. Persons and contracts that did not fulfill the inclusion criteria (among them 200.507 contracts with companies that could not be assigned to one single person) were excluded. The final cohort of more than 420.000 individuals is among the largest ones worldwide in the field of cell phone use.

No elevated cancer risk by mobile phone use in the period until 1996

The central Danish population registry and the Danish cancer registry provided information on the cancer cases in the cohort. The observed incidence of cancers in the cohort was compared with the incidence in the Danish population. From these data scientists could calculate whether mobile phone users had a higher risk of cancer.

In 2001, the results of the first analysis for the period until 1996 were published in the Journal of the National Cancer Institute. It showed no correlation between mobile phone use and cancer risk.

Follow-up until 2002: no increased cancer risk for mobile phone users

Due to the short observation period, only few cancer cases in long-term users could be detected by the time of the first analysis. The follow-up period was extended by six years to 2002. In December 2006, the results were again published in the Journal of the National Cancer Institute.

Even for the prolonged observation period, there was no evidence for an increased tumor risk due to cellular telephone use among either short-term or long-term users (more than ten years). Considered cancers were brain tumor, salivary gland tumor, acoustic neuroma, eye tumor, and leukaemia.

The study has, however, some methodological limitations:

mobile phone users whose contract was negotiated by a company were excluded – that could, however, be the heavy users

the comparison group - the Danish general population - consisted not only of non-users

it cannot be excluded that phone subscribers didn’t use it themselves, but passed their phone to others

potential confounders could not be assessed and considered.

These limitations restrict the validity of the study.

Prolonged follow-up period until 2007: no increased cancer risk for mobile phone users

In 2011, the first results of the extended study follow-up to 2007 were presented in the British Medical Journal. The focus was on the statistical analysis of possible brain cancers. In 2013, results for skin cancer in this follow-up period were published in the American Journal of Epidemiology. Neither analysis showed an increased risk of cancer for mobile phone users.

Results are consistent with those of other epidemiologic studies

Overall results are quite consistent with those of other epidemiologic studies that to a large extent found no increased cancer risk in the first ten years of mobile phone use.

Still unclear is the situation for long-term users, even after the so called INTERPHONE study, the largest study on the risk of brain tumors in relation to mobile phone use conducted to date. It investigated a large number of individuals who used mobile phones for more than 10 years. Overall, no increased risk of glioma and meningioma was found in association with mobile phone use. The group of long-term and intensive users showed signs of a potentially increased risk of gliomas.

Since also the INTERPHONE study has methodologic weaknesses, the question on elevated brain cancer risks after long-term usage of mobile phones cannot be answered at this time.